Radar decoy designers have the challenge of producing a decoy having a radar cross section which simulates moving and stationary objects of various sizes. This decoy must also simulate the radar cross section of objects exposed to a broad range of frequencies since various tracking radar used different radar frequencies.
Conventional decoys have included chaff released from a moving airplane. The problem with chaff is the strands become nearly motionless once released from the moving airplane. This motionlessness can easily be detected by conventional radar to distinguish the decoy from the moving airplane. Consequently, an effective decoy must simulate the target""s radar cross section and movement over a wide range of radar frequencies.
Earlier radar decoys used a variety of techniques. The Lewis device, U.S. Pat. No. 3,380,464, achieved radar wave reflectivity by varying the conductivity of incremental reflective elements. The patented device included a large number of elements and is complex and costly. The Lewis device includes a sandwich-like reflector made of dielectric and metallic materials. The device is effective only with single polarities. The invention, unlike the Lewis device, is simpler, less costly, and uses a simple metallic reflector which is effective with radar waves having vertical and horizontal polarities components.
The Williston device, U.S. Pat. No. 3,142,059, like the Lewis device, is effective with only one radar wave polarization. Additionally, the Williston device is a mechanical design having rotary components driven by a motor. The effective radio frequency bandwith is considerably more narrow than the invention""s radar decoy. Consequently, the Williston device will not simulate large and small radar cross section objects like aircraft and tanks.
The devices disclosed in the Lewis Patent, U.S. Pat. No. 3,417,398, the Wheeler Patent, U.S. Pat. No. 3,896,440, and the Onoe Patent, U.S. Pat. No. 4,314,249, are distinguishable from the invention""s radar decoy by having limited radio frequency applicability, limited radar cross section simulation, and single radio frequency polarity sensitivity.
The invention is a radar decoy. The decoy is an electronic simulator of objects which generates radar detectable signals over the entire microwave frequency range. The simulator includes a series of tuned, spaced, diode networks for generating carrier suppressed doppler sidebands. Each diode network is tuned to a single, different frequency so the decoy has the wide frequency range.
Each diode network is a bow-tie dipole antenna with a beam lead PIN diode connected across the antenna. Microstrip inductors are connected between each dipole antenna to radio frequency isolate each antenna from an adjacent antenna. An advantage of this antenna design is the radar decoy is effective with radio frequency waves having vertical and horizontal components. Many existing radar decoys are only effective with radio waves having a single polarization.
The diode networks are mounted in a pyramid shaped corner reflector having an open side. The corner reflector is typically made of a metallic sheet or of a material having an electrically conductive coating. The diode networks interact with the corner reflector to modulate the amplitude and phase of impinging radar signals.
The diode networks and corner reflector system simulate a moving target by generating a frequency having a doppler frequency shift. This frequency is controlled by a switching circuit which turns the diode networks on and off at a selected frequency.
An object of the invention is to be a radar decoy by simulating the radar signature of moving and stationary targets.
A feature of the invention is the radar decoy is expendable.
A second feature of the invention is the radar decoy operates over several octaves of frequency.
A third feature of the invention is the radar decoy modulates and reflects carrier frequencies up to 20 GHz compared to much lower frequencies for existing radar decoys.
A fourth feature of the invention is the radar decoy has improved modulation depth to better simulate a moving target.
A fifth feature of the invention is the radar decoy includes amplitude and phase modulation compared to conventional radar decoys which use only amplitude modulation.
An advantage of the invention is the improved simulation of moving and stationary targets making the radar decoy a more effective protector of the target simulated by the decoy. This enhanced effectiveness improves the survivability of the intended target against attacks from aircraft, missiles, or other radar guided interceptors.